Kinematics and structure of submarine landslides;recent learnings from 3D seismic reflection data

Submarine landslides (slides) transport very large volumes of sediment (up to 250,000 km 3 ) from the world's continental margins to the adjacent deep oceans. Their size and frequency mean that slides can dominate the stratigraphic record of many continental margins. Slides pose a threat to costly infrastructure, and pose a threat to human life via the generation of tsunamis. Field data, near-seabed geophysical imaging, and borehole data provide insights into slide composition and geotechnical properties. These data are often spatially limited, which is problematic given the very large size of some slides. Critically, these data do not permit detailed analysis of the three-dimensional structure of slides, from which we may infer the kinematics of the parent flows. Here we highlight some recent advances in our understanding of slide structure and kinematics derived from 3D seismic reflection data from offshore Australia, Uruguay, Indonesia, and the Gulf of Mexico. These data allow us to map individual structures within the proximal (head), translational, and distal (toe) domains at relatively high-resolution (<10 m). Data from Uruguay appear to show diffuse extension in the head domain, best-described as shear-thinning. In contrast, data from offshore Australia image a head domain defined by classic brittle extension, associated with the formation of internally undeformed, 1-5 km wide and >50 km long fault-bound blocks that are flanked by fluid escape structures. Translational domains, rather than being dominated by a relatively rigid, singular mass, are commonly composed of numerous `cells' that are several kilometres wide, and which are bound by sub-vertical diffuse shear zones or discrete strike-slip faults. We infer cells document spatial variations in the downslope velocity of the translating mass, in one case related to the presence of intra-slide megaclasts. Data from Indonesia show frontally-emergent and frontally-confined toe domain styles are not mutually exclusive, but can pass along-strike into one another over very short distances (<1 km), even for slides emplaced by only relatively minor horizontal translation (c. 1 km). Our observations highlight how 3D seismic reflection data can contribute to improving our understanding of slide kinematics, and associated hazards.